It's the 2 clicks. Tires are the first thing you see when you enter the setup screen.
I think it remains confusing anyway.
For exemple, for a GT5 race car,
- In the car set-up screen, you can select "Automatic per weather","GT5 rain", or "GT5 slick"
- In the pit stop strategy, you have a more detailed list: Intermediate, Wet, full wet, soft, medium and hard
The game allows what seems to be inconsistencies (GT5 rain in car set-up and slick soft in strategy for exemple).
You can also set the tyre pressure in both screens and if you have different values, I do not know which one takes the priority.
One could think that the "pit strategy" only sets the tyres you will get after pitting, not at the start of the race.... but it is not that easy, this screens also impacts the tyres you start with.
.... I would be very pleased to get a detailed explanation on how all this interacts. I guess that there is a logic behind it and that once you know it, you can set your car and strategy efficiently. I am just saying that it is far from self explanatory.